Applicant claims, under 35 U.S.C. xc2xa7119, the benefit of priority of the filing date of Feb. 20, 1999 of a German patent application, copy attached, Ser. No. 199 07 326.0, filed on the aforementioned date, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an angle measuring system, in particular an angle measuring system without its own bearing.
2. Discussion of Related Art
High-precision angle measuring systems with a shaft in the measuring system and a corresponding independent bearing of the shaft are known for instance from the book entitled xe2x80x9cDigitale Lxc3xa4ngen- und Winkelme technikxe2x80x9d [Digital Length and Angle Measuring Technology] by A. Ernst, Verlag Moderne Industrie, 3rd edition, 1998, pp. 61-64. To achieve the requisite measuring accuracy, high-precision bearings, which are correspondingly expensive, by way of which the shaft is supported are required in the angle measuring system. Via a suitable coupling, the shaft is connected to a graduation disk that carries the radial measurement graduation. The measurement graduation is in turn scanned by means of stationary scanner units in the angle measuring system to generate angle-dependent output signals. For further processing, the angle-dependent output signals are transmitted, for instance in the form of sine-wave incremental signals, to a downstream evaluation unit.
From the same book, pages 64-70, angle measuring systems without their own bearing are also known, in which a rotationally symmetrical measurement graduation or a corresponding graduation disk is disposed directly on a rotating shaft. One or more scanner units are provided stationary relative to the rotating graduation disk, and by way of them the measurement graduation is scanned, for instance photoelectrically. In such systems, the scanner units are not fixedly disposed relative to the graduation disk or measurement graduation but instead have to be correctly aligned to it during assembly, which involves corresponding effort and expense for calibration. It is also not assured a priori in these angle measuring systems that the axis of rotation of the rotating shaft will coincide with the axis of the graduation disk; that is; there may possibly be some eccentricity or a tumbling motion of the rotating graduation disk, which in turn leads to erroneous measurements. It has therefore already been proposed that the resultant errors in eccentricity be eliminated with the aid of a plurality of separate scanner units. In this connection, European Patent Disclosure EP 0 325 924 B1 of the present applicant can for instance be named. Nevertheless, in this case again, exact calibration of the scanner units relative to the rotating measurement graduation is required.
So-called preassembled built-in rotary angle encoders are also known, which again have no bearing of their own and in which one or more scanner units include a stationary part and serve to scan the graduation disk that is disposed on a rotating shaft. In these systems as well, as with the angle measuring systems without their own bearing mentioned above, high-precision calibration of the scanner units relative to the rotating measurement graduation is necessary.
It is therefore an object of the present invention to disclose an angle measuring system that performs as well as much as possible without a complicated bearing of its own and nevertheless permits high-precision, error-free detection of the angular position of a rotating object. The angle measuring system should be as simple as possible to assemble, without major effort or expense for calibration.
This object is attained by an angle measuring system for high-precision determination of the angular position of an object, the system including a stationary component unit, a rotationally symmetrical measurement graduation that is connected to an object that rotates about an axis of rotation (R) and a plurality of scanner units that are disposed in a defined three-dimensional orientation in the stationary component unit and serve to scan the measurement graduation at a plurality of different measurement graduation sites and generate angular-position-dependent fractional scanning signals. The system includes a correction system that receives the fractional scanning signals of the scanner units and generates angle-dependent output signals that are freed of errors that result from a possibly occurring nonagreement of the axis of rotation (R) of the object with an axis of symmetry of the measurement graduation.
The provisions according to the invention now make it possible to achieve a high-precision angle measuring system without its own complicated bearing. Instead, the existing bearing of the rotating object or the corresponding shaft, whose angular position is to be detected, is utilized for the rotating measurement graduation as well. This may for instance be a rotary table on a machine tool.
Calibration and assembly problems relating to the correct positioning of the scanner units with respect to the rotationally symmetrical measurement graduation are also eliminated, since the scanner units are already preassembled in a component unit by the manufacturer. Because of the provisions to be described in detail hereinafter, no further calibration of the scanner units after they are installed on a rotating shaft has to be done by the user.
Any eccentricity errors that may be present, caused for instance by the imperfect concentricity of a shaft, are corrected by the use according to the invention of correction means in the angle measuring system. Certain scanning arrangements with a plurality of scanning fields and certain signal processing elements in the angle measuring system function as the correction means here. The angle measuring system of the invention accordingly generates one or more angle-dependent output signals that have no eccentricity errors.
Within the scope of the present invention, it is understood that along with the exemplary embodiment described below, the most manifold further variant embodiments are also possible.
For instance, the type of scanning is not limited to optical or photoelectric systems; alternatively, other physical scanning principles can be employed to scan the measurement graduation, such as inductive, capacitive or magnetic scanning principles.
Along with scanning the graduation disk, it is understood that so-called drum scanning can be performed on the basis of the concepts of the invention. Besides the embodiment as a transmitted light system, an embodiment as an incident light system with a reflective measurement graduation can also be realized at any time.
Along with one or more incremental measurement graduations, additional tracks next to the measurement graduation can also be provided, which for instance carry coded reference markings to identify absolute positions, and so forth.
Manifold options also exist as to the form in which the output signals, free of errors of eccentricity, are transmitted to the downstream evaluation unit. For instance, transmission in analog sine-wave form or in the form of digital square-wave signals or in serially encoded form is possible. In particular this last form of data transmission makes it possible to transmit further additional information from the angle measuring system of the invention to the evaluation unit.
Further advantages along with details of the angle measuring system of the invention will become apparent from the ensuing description of exemplary embodiments in conjunction with the accompanying drawings.